The present invention relates to a fade-in and fade-out device of an automatic servomechanism of diaphragm in a cinecamera, and, more particularly, to a fade-in and fade-out device in which the exposure in the midpoint of the time required for the fading-in and for the fading-out is made equal to each other.
The applicant has already proposed in Japanese Patent Appln. No. 82265/74 filed on July 19, 1974 a fade-in and fade-out device wherein the output voltage of a scene light indicating voltage generating circuit including a photoelectric element located behind the objective lens diaphragm or a diaphragm coupled thereto so as to receive scene light therethrough and the output voltage of a reference voltage generating circuit including a capacitor are compared with each other so that the objective lens diaphragm is actuated by the voltage differential between both output voltages until both output voltages are made equal to each other by virtue of a servomotor energized by the voltage differential being coupled with the diaphragm, the fade-in and fade-out device comprising a constant current charging circuit and a constant current discharging circuit selectively connectable to the capacitor of the reference voltage generating circuit for selectively charging and discharging the capacitor, and a switch adapted to selectively connect either of the charging or discharging circuit to the capacitor, thereby permitting the reference output voltage of the reference voltage generating circuit to be linearly varied with the lapse of time when the capacitor is selectively charged or discharged with the constant current available from the constant current charging or discharging circuit so that the exposure at the midpoint of time required for the fading-in and fading-out is made equal to each other.
In such a device, however, it is necessary to vary the value of the constant charging or discharging current of the constant current charging and discharging circuit to be charged to or discharged from the capacitor in order to vary the time of fading-in or fading-out. Such a measure is very difficult in adjustment and setting thereof.